1. Field of the Invention
The present invention relates to a system and method for controlling emission of Volatile Organic Compounds (VOCs) and, more specifically, to an improved system and method for controlling VOC emissions by combustion of such emissions in an internal combustion engine.
2. Description of the Related Art
The direct release of Volatile Organic Compounds into the atmosphere has been for some time now recognized as a primary contributing factor in affecting ozone levels in the lower atmosphere. The EPA has established standards for safe levels of ozone, and local air quality districts have implemented regulations and mandated control measures pertaining to the release of hydrocarbon vapors into the atmosphere, from operations such as soil remediation and storage tank inerting, and storage vessel loading and unloading; that have been identified as sources of hydrocarbon emissions responsible for impacting ozone levels.
The process of treating these vapors, through any of a variety of methods, is typically referred to as degassing; which is either the collection or on-site destruction of these vapors as an environmentally responsible alternative to their otherwise direct release into the atmosphere.
The internal combustion engine, as well as open-flare incinerator units, has been employed for several decades as a means of on-site destruction of these Volatile Organic Compounds by elemental combustion. The combustion process does give rise to the undesirable production of carbon monoxide and nitrogen oxides; however this has been accepted as a reasonable consequence for the nearly 99% efficiency in the destruction of hydrocarbon based VOC's. These consequential emissions are accepted, but tolerated only to a regulated extent, and are also a factor to be considered in engines and incinerators employed in vapor destruction applications.
Combustion efficiency is often of equal importance to that of volumetric throughput in internal combustion engines employed in vapor destruction applications. For example, many of the Volatile Organic Compounds being the subject of treatment were never intended for use as a motor fuel. At one extreme of the range are the lighter C2 through C7 aliphatic or branched hydrocarbons and their corresponding alcohols; that tend to exhibit lower heating values (btu/cu ft) yet higher octane ratings than their contrasting counterparts such as gasoline with a substantially higher heating value yet lower octane rating ; rendering these later compounds more susceptible to abnormal combustion and undesirable emissions. This is a particular concern involving combustion within the internal combustion engine versus that of the open-flare incinerator type unit.
In the case of the open-flare incinerator type unit, all of the energy derived from the combustion process is emitted as thermal energy. In the case of the internal combustion engine, a certain portion of the energy is dissipated through the engine cooling system; however a considerable amount remains as mechanical energy at the end of the rotating crankshaft. The maximum achievable volumetric throughput of the internal combustion engine is limited by the amount of produced horsepower that can be put to use at the flywheel.
Various methods have been employed throughout the past in an effort to impose a load at the engine flywheel such to match the power output in an effort to provoke the engine to realize its ideal potential volumetric throughput. Amongst these methods, has been the coupling of external devices such as hydraulic pumps, roots blowers, electrical generators and others; in an endeavor to impose some means of load to the rotating crankshaft. One common shortfall in employing such devices, is that their operable range does not match the inherently wider operable range (RPM) of the internal combustion engine; and their employment has served either to limit the maximum RPM of the engine, or otherwise require complex gear reduction type drives necessary to keep the RPM of these ancillary driven loading devices within safe operating speeds.